Traditionally, aromatic compounds in lube range products are removed through hydrogenation or cracking chemistry. While the hydrogenation process may be able to remove a large of amount of the aromatics from lube base stocks, large multi-ring aromatics cannot be completely hydrogenated leaving at least one ring aromatics left in the product. Such one ring aromatic may cause issues with additive package solubility and/or stability used in the formulated lube product or introduce oxidative instability causing coloring of the final product. In some instances, these large compounds can be cracked open exposing the inner aromatics rings which can then be hydrogenated; however, cracking chemistry can be non-selective thereby cracking desired high molecular weight molecules resulting in product yield loss and potentially lower performance of the base stock. Thus, there is a need for a separation process (e.g., adsorption) that can separate aromatic compounds from lube base stocks. Furthermore, coupling a separation process with conventional hydroprocessing processes may produce base stocks with higher saturate levels. Highly saturated base stocks are desired in the industry since it is believed that the unsaturated species can cause significant oxidative degradation of the finished lubricants under the operating conditions found in typical engines and industrial applications.
Porous inorganic solids have found great utility as separation media for industrial application. In particular, mesoporous materials, such as silicas and aluminas, having a periodic arrangement of mesopores are attractive materials for use in adsorption and separation processes due to their uniform and tunable pores, high surface areas and large pore volumes. Such mesoporous materials are known to have large specific surface areas (e.g., 1000 m2/g) and large pore volumes (e.g., 1 cm3/g). For these reasons, such mesoporous materials enable molecules to rapidly diffuse into the pores and therefore, can be advantageous over zeolites, which have smaller pore sizes. Consequently, such mesoporous materials can be useful as large capacity adsorbents.
However, mesoporous organosilicas, which may be used as an adsorbent, are conventionally formed by the self-assembly of the silsequioxane precursor in the presence of a structure directing agent, a porogen and/or a framework element. The precursor is hydrolysable and condenses around the structure directing agent. These materials have been referred to as Periodic Mesoporous Organosilicates (PMOs), due to the presence of periodic arrays of parallel aligned mesoscale channels. For example, Landskron, K., et al. [Science, 302:266-269 (2003)] report the self-assembly of 1,3,5-tris[diethoxysila]cylcohexane [(EtO)2SiCH2]3 in the presence of a base and the structure directing agent, cetyltrimethylammonium bromide, to form PMOs that are bridged organosilicas with a periodic mesoporous framework, which consist of SiO3R or SiO2R2 building blocks, where R is a bridging organic group. In PMOs, the organic groups can be homogenously distributed in the pore walls. U.S. Pat. Pub. No. 2012/0059181 reports the preparation of a crystalline hybrid organic-inorganic silicate formed from 1,1,3,3,5,5 hexaethoxy-1,3,5 trisilyl cyclohexane in the presence of NaAlO2 and base. U.S. Patent Application Publication No. 2007/003492 reports preparation of a composition formed from 1,1,3,3,5,5 hexaethoxy-1,3,5 trisilyl cyclohexane in the presence of propylene glycol monomethyl ether.
However, the use of a structure directing agent, such as a surfactant, in the preparation of an organosilica material, requires a complicated, energy intensive process to eliminate the structure directing agent at the end of the preparation process. For example, calcining may be required as well as wastewater disposal steps and associated costs to dispose of the structure directing agent. This limits the ability to scale-up the process for industrial applications.
Therefore, there is a need for improved processes for separation of aromatic compounds from hydrocarbon feeds using organosilica materials that can be prepared by a method that can be practiced in the absence of a structure directing agent, a porogen or surfactant.